1. Field of the Invention:
The present invention relates to a method of removing BCl.sub.3, Cl.sub.2, AlCl.sub.3, HCl or the like from waste gas discharged from chemical dry etching processes using chloride and/or chlorine containing gases in the semiconductor industry, to thereby making these waste gases harmless.
2. Description of the Prior Art:
It is feared that environmental pollution may be caused by a large variety of harmful gases which are used in semiconductor manufacturing processes in the semiconductor industry. Chloride and/or chlorine containing gases which are contained in waste gas discharged from chemical dry etching processes using chloride and/or chlorine containing gases are extremely harmful to the human body, and therefore it is urgent to establish an effective system for removing such harmful components from the waste gas.
Various kinds of methods of removing chloride and/or chlorine containing gases have heretofore been proposed. These known methods may be roughly divided into two types, that is, wet treating method and dry treating method.
In the wet treating method, waste gas and a cleaning solution which is generally an alkaline aqueous solution, e.g., NaOH, are brought into countercurrent contact with each other in a gas-liquid contact apparatus such as a packed tower or a spray tower to thereby neutralize and absorb harmful chloride and/or chlorine containing gases.
This type of treating method suffers, however, from the following problems: the cleaning solution may flow back to the etching equipment; the waste gas treating apparatus may be clogged with a reaction product; and the treating efficiency is low.
The dry treating method employs a solid treating agent to remove harmful waste gases, and there are two different types of dry treating method, that is, one that employs an agent carried on active carbon as a treating agent for chloride and/or chlorine containing gases [see Japanese Pat. Public Disclosure No. 61-35849 (1986)], and the other that employs an alkaline treating agent alone, that is, without any carrier or the like [Japanese Pat. Public Disclosure No. 61-61619 (1986)].
In the dry treating method, a treating agent is packed in a packed tower and waste gas is passed through the tower to remove harmful components from the waste gas. In this type of method, the operation is simpler and the system is simpler and smaller than in the case of the wet treating method, but the method suffers from the following problems.
The waste gas discharged from chemical dry etching processes using BCl.sub.3 and Cl.sub.2 contains at least two different kinds of chloride and chlorine containing gas, i.e., BCl.sub.3 and Cl.sub.2.
When a gas mixture of BCl.sub.3 and Cl.sub.2, is treated by the dry method, BCl.sub.3 and Cl.sub.2, are adsorbed by the treating agent in different amounts, respectively. More specifically, in either case where a treating agent carried on active carbon is used or an alkaline agent alone is employed as a treating agent, the adsorptive capacity for either BCl.sub.3 or Cl.sub.2, is large, but that for the other is small.
For this reason, when dry etching waste gas is treated, if the load of a gas for which the adsorptive capacity of the treating agent is smaller is high, this gas breaks through in a relatively short period of time and therefore the cycle of replacement of the treating agent in the packed tower is shortened, which results in an increase in the amount of treating agent used.